The fine structure of the mature Bruch's membrane is well established, however, its development has received little attention in previous publications. The purpose of this proposed research program will be to thoroughly examine the fine structural development of the fibrous connective tissues within Bruch's membrane of the vertebrate eye. The observations will be obtained by means of transmission electron microscopy. The normal fine structure of the various developing fibrous connective tissues will first be observed. Experimental embryos will then be exposed to various enzymes known to specifically digest certain of the fibrous connective tissues. Exposure to enzymes will occur either before ("living" specimens) or after fixation ("fixed" specimens). In some experiments ruthenium red will be dissolved in the fixative. All tissues will be fixed in buffered aldehydes, dehydrated in ethanol and otherwise prepared for conventional electron microscopy. A specific metallic prophyrin stain will be used to identify elastin. The acquired morphological and chemical data will enable further understanding of the developmental relationships among the various fibrous connective tissues.